1. Technical Field
The present disclosure relates to semiconductor devices and methods for fabricating the same.
2. Description of the Related Art
Wide-bandgap semiconductors are applied to various semiconductor devices such as power devices, devices with enhanced environmental resistance, high-temperature operating devices, and high-frequency devices. Among such devices, attention has been directed to applications to power devices such as switching devices and rectifying devices.
Among wide-bandgap semiconductors, silicon carbide (SiC) is a semiconductor material that enables relatively easy fabrication of a substrate and also enables formation of a silicon dioxide (SiO2) layer, which is a high-quality gate insulating layer, by thermal oxidation. In view of this, power devices using SiC have been actively developed (see, for example, Japanese Unexamined Patent Application Publication No. 2012-151400).
Examples of a switching device for a power device using SiC include a metal insulator semiconductor field effect transistor (hereinafter referred to as a “MISFET”) and a metal semiconductor field effect transistor (hereinafter referred to as a “MESFET”).
The electrical breakdown field and thermal conductivity of SiC are higher than those of Si. Thus, a SiC power device using SiC can increase the breakdown voltage and reduce a loss more easily than a Si power device. In the case of obtaining the same performance as the Si power device, the SIC power device can significantly reduce the device area and thickness, as compared to the Si power device.
As the device area and thickness decrease, the parasitic capacitance of a gate electrode with respect to a substrate decreases. SiC has a higher electron saturation velocity than that of Si. By utilizing these advantages, the SiC power device performs a switching operation at a much higher speed than the Si power device.
To obtain a SiC power device that can operate at high speed while taking advantages of the above-described features, Japanese Unexamined Patent Application Publication No. 2012-151400 describes a SiC power device including a gate insulating layer with a double-layer structure of an oxidized layer doped with phosphorus and an insulating layer for reducing diffusion of phosphorus. Japanese Unexamined Patent Application Publication No. 2012-151400 describes that this structure reduces the interface state density at the interface between a silicon carbide semiconductor layer and the insulating layer and, thereby, increases on mobility.